The present invention relates to electronic cameras and to methods and intermediate structures useful in forming the same.
An electronic camera module includes an optoelectronic sensor which includes an array of sensitive elements capable of converting light to electrical signals and optical elements for focusing an image of a scene to be captured onto the array. Most commonly, the sensor includes a semiconductor imaging chip incorporating charged coupled device (“CCD”) elements or other optically sensitive elements such as p-n junctions in a CMOS structure. Each element is capable of capturing one picture element or “pixel” of the image. The imaging chip typically also includes conventional circuitry for converting the signals from the elements into a stream of data representing the image. The sensor may include either an imaging chip alone or an imaging chip together with a transparent cover which protects the sensitive elements from dust particles. There has been substantial progress in development of such sensors during the last few years; modern sensors may incorporate hundred of thousands of elements or “pixels” within a few square centimeters of chip surface area. Therefore, it has become practicable to incorporate digital cameras into devices such as cellular telephones, personal digital assistants or “PDAs” and the like. Camera modules for incorporation in such devices should be both compact and economical to manufacture.
As the size of sensors has diminished, and their capability has increased, there has been an increasing demand for improvements in the associated optical components such as lenses and in the structures and techniques used for mounting the optical components in position relative to the sensors. Moreover, the sensors and optical components must be mounted to elements of a larger assembly. Typically, the sensor is electrically connected to a printed circuit board or other circuit panel using techniques such as wire-bonding or surface-mounting. The design of the optical components and supporting structures must accommodate such electrical connections and must fit within a small volume and within a small area on the circuit panel.
It has been proposed heretofore to provide electronic cameras with so-called liquid lenses. As described, for example, in Kuiper et al., “Wet and Wild,” SPIE OEMagazine, January 2005, it has been proposed to provide a lens having a refractive interface defined by two immiscible liquids in a container. One of these liquids typically is an electrically conductive liquid such as salt water, whereas the other liquid typically is a dielectric liquid such as a silicone oil. The two liquids have different refractive indices. Electrodes are provided in proximity to the container, with one electrode in contact with the conductive liquid, and with the opposite electrode extending along the circumferential wall of the container. The circumferential electrode is covered by a thin film of a dielectric solid. An electrical potential applied between the electrodes causes a phenomenon known as electrowetting, which, in turn, causes a change in the curvature of the interface or meniscus formed by the immiscible liquids. This, in turn, changes the curvature of the refractive interface. Such a structure provides an optical element having refractive properties which vary with the applied voltage. As described in the aforementioned Kuiper et al. article, such a refractive element can be used to provide a compact variable focus optical system for an electronic camera.
Variable optical elements which operate by electrowetting consume only miniscule amounts of electrical power during operation, on the order of a microwatt. However, this power must be provided in the form of signals on the order of 30-100 volts to control the shape of the meniscus. The other circuits included in devices such as cell phones and PDA's typically use about 3 to 5 volts supplied by a battery or low-voltage power supply circuit. Therefore, a special voltage-converting power supply must be provided in conjunction with the variable optical element. The voltage converting power supply circuits used heretofore have incorporated elements such as discrete transistors and inductors. These circuits are bulky, and thus substantially increase the space required for the camera. Moreover, these circuits add considerable cost and complexity to the assembly.